Fix errors with clang

Examples/OldDrawGrid/input.cpp

 #include "input.h"
 #include "inc_glut.h"
+#include <stdlib.h>
 
 Input::Input(int * val, std::string comment) : comment(comment) 
 { 

Examples/OldDrawGrid/printtext.cpp

 #include "inc_glut.h"
 #include <stdarg.h>
 #include <stdio.h>
+#include <string.h>
 void printtext(const char * fmt, ...)
 {